Implant pellets and methods for performing bone augmentation and preservation

ABSTRACT

Embodiments described herein are related to pellets that are placed within an extraction site that is in need of bone augmentation and preservation. The pellets are typically cylindrical in shape and comprise a material and a polymer coating. The pellets may advantageously facilitate sufficient new bone growth that jaw bone deterioration is prevented. The pellets create, arrange, and assemble an ideal growth environment for new bone growth to rapidly grow and preserve the original contours of an individual&#39;s jaw bone.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/785,077, filed Oct. 16, 2017, now allowed, which is a continuation ofU.S. patent application Ser. No. 15/090,201, filed Apr. 4, 2016, nowU.S. Pat. No. 9,814,544, which is a continuation of U.S. patentapplication Ser. No. 13/362,807, filed Jan. 31, 2012, now U.S. Pat. No.9,301,816, which is a divisional of U.S. patent application Ser. No.12/350,754, filed Jan. 8, 2009, now U.S. Pat. No. 8,128,706, whichclaims the benefit from U.S. Provisional Application No. 61/006,372,filed on Jan. 9, 2008, each of which is incorporated herein in itsentirety by express reference thereto.

FIELD OF THE INVENTION

Embodiments described herein relate generally to apparatuses and methodsfor dental surgery, and particularly to apparatuses and methods forperforming bone preservation and/or augmentation.

BACKGROUND OF THE INVENTION

When an extracted or otherwise missing tooth is not immediately graftedor replaced with an implant, atrophy of the alveolar bone or jaw boneoccurs over time. Consequently, individuals who have been partiallyedentulous for an extended period of time are left with an atrophicalveolar ridge that cannot securely support a denture. Furthermore, theedentulous individual faces deteriorated aesthetics and a compromisedability to chew and must be rehabilitated leaving the quality of theindividual's oral health in an unfortunate state.

The buccal and lingual portions of the alveolar bone are composed ofsoft trabecular bone which has the unique characteristic of beingcapable of absorbing the shocks caused by the movement of teeth duringspeech, eating, etc. The removal of a tooth and the resulting absence ofthe bone pressure stimuli in the area causes the alveolar bone to resorbin that area. The result can be loss of 40-60% of the alveolar ridge'sformer height. After this initial 40-60% loss, the alveolar bone cancontinue to resorb at a bone loss rate of 0.5-1.0% per year.

In addition, when teeth are extracted, the lack of supporting bone failsto sufficiently support the load of a later inserted prosthesis orimplant. This is a byproduct of the alveolar bone becoming weaker due tothe lack of internal stimulation leading to a softer, porous, lessdense, and spongier nature of the deteriorated bone. In addition, dentalimplants are prone to fail due to the porous nature of the bone and alack of bone density.

Improved materials and techniques for augmenting, preserving andsupporting bone growth are needed to decrease alveolar ridgedeterioration and enhance the alveolar bone support of an oralprosthesis or implant.

BRIEF SUMMARY OF THE INVENTION

Embodiments described herein include a device called a pellet that iseither placed within a fresh extraction site of the gum or onlayed onexisting bone tissue. The pellet is designed to facilitate boneformation (preservation or augmentation) within the tooth socket. Thepellet can be of various lengths, widths and shapes depending on the jawbone deficiency. The pellet comprises one or more biocompatiblematerials having a polymer coating or a combination composite coatingconsisting of polymers and other biomaterials (degradable ornondegradable). The one or more biocompatible materials are arranged orassembled into a solid, matrix or mesh-like structure designed toenhance a bone growth environment by osteoinduction or osteoconduction.After insertion, the pellet facilitates new bone growth formation forpreservation and/or augmentation. Over time, an integrated bone tissue,which is the obtained integration between the growing bone and thepellet, develops. Once adequate bone growth has occurred, the integratedbone structure can support a prosthesis or can be cored to create anopening, which can accommodate an implant device. Thus, the resultingfoundation can provide enhanced support, fixation, and anchoringstrength for a prosthesis or implant device due to the preservationand/or augmentation of the bone tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a cross-sectional portion of a pellet in accordancewith a first embodiment discussed herein.

FIG. 1B illustrates a cross-sectional portion of the pellet inaccordance with a second embodiment discussed herein.

FIG. 2 illustrates a cross-sectional portion of the pellet in accordancewith a third embodiment discussed herein.

FIGS. 3-5 illustrate various stages of performing bone augmentation inaccordance with an embodiment discussed herein.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments discussed herein provide techniques and pellets forpreserving and augmenting bone growth particularly well suited fordecreasing alveolar ridge deterioration and enhancing support of aprosthesis. In the following description, numerous specific details areset forth, such as material types, dimensions, specific tissues, etc.,in order to provide a thorough understanding of the present invention.Practitioners having ordinary skill in the biomedical arts willunderstand that the invention may be practiced without many of thesedetails. In other instances, well-known devices, methods, andbiochemical processes have not been described in detail to avoidobscuring the claimed invention.

As described above, one problem associated with the failure of aprosthesis is the inability of the surrounding bone to support the loadof the implant. This is especially true in areas that are weaker due tothe softer, porous, less dense, or spongier nature of the alveolar boneor jaw bone. In particular, dental implants are prone to fail due tolateral, anterior or posterior movement of the prosthesis together withlack of a rigid surrounding bone structure. This problem similarlyaffects the stabilization of a tooth implant or prosthesis.

Another problem with the failure of a prosthesis is due to adeteriorating jaw bone. When an extracted or otherwise missing tooth isnot immediately grafted or replaced with an implant, atrophy of the jawbone occurs over time resulting in compromise esthetics and compromisedability to function.

Embodiments discussed herein offer solutions to the foregoing problemsby providing pellets that can be placed into a cavity of bone to enhancethe structural integrity, reduce bone deterioration, and protect theoriginal (pre-extraction) shape of the bone itself. According to oneembodiment, a pellet comprises a material arranged in a structured,matrix manner. After inserting the pellet into a cavity of bone, naturalinfiltration occurs as a result of and facilitated by the pellet'sinsertion such that new bone growth fills the internal cavity andreplaces biodegradable portions of the pellet. Alternatively, the bonegrowth may fill internal pores of the pellet formed by the matrix natureof the pellet. The material comprising the pellet functions as an idealgrowing environment for newly formed bone. By using means such as thepellet, new bone growth will occur (at an accelerated pace if seeded orgrow at a normal pace if unseeded), as explained in greater detailbelow. The new bone growth can be used to support a prosthesis ordenture with enhanced stability compared to a prosthesis or implantwithout such bone growth.

Optionally, the resulting integrated bone structure of the pellet can becored or otherwise shaped to create an opening to accommodate an implantdevice. The pellet typically has a cylindrical lateral cross sectionalshape but may take on any shape that facilitates bone augmentationand/or preservation depending on the jaw bone or skeletal deficiency.For example, in addition to cylindrical, the shape of the pellet mayhave a cross-sectional shape that is elliptical, rectilinear, round,etc. The shape of the pellet can also be tailored to fit the exactdimensions of the cavity. It should be appreciated that the preciseshape of the pellet should not be limited to examples described above.The shape of the pellet, however, is usually slightly smaller indiameter than the receptor site or the site of extraction. It should benoted that where the site of extraction is smaller than the pellet,surgery may be needed to increase the size of the receptor site.Optionally, surgery may be required to “clean” the site (e.g., removalof extra tissue and/or bone fragments, etc.). Optionally, the pellet canbe specifically designed for simple insertion into the receptor site.For example, careful measurements of the receptor site can be taken, andthe pellet can be created for the particular receptor site. Measurementssuch as, for example, “casts” can be taken as known in the art. Thepurpose of the pellet is to preserve bone tissue and facilitate new bonegrowth such that jaw bone deterioration is prevented. Another purpose isto minimize the loss of bone volume. These goals are achieved by placingthe pellet into the defect, and creating, arranging, or assembling anideal growth environment to facilitate new bone growth and preserve theoriginal contours of an individual's jaw bone tissue. The arrangement ofthe materials within the pellet may be entirely random or may consist ofa fabric-like pattern having a more regular, organized blueprint. Forexample, conventional 3D printing manufacturing methods (describedbelow) can be used to create fabric-like patterns and are consideredacceptable for producing the pellet of the present invention.

With reference to FIGS. 1A-1B where like elements are designated by likenumerals, various steps in the preparation of the material utilized, inaccordance with one embodiment of the invention, to form the pellet areillustrated. FIG. 1 A shows a portion of the pellet 100 that comprises amaterial 102. The material 102 is a degradable or non-degradablebioceramic material, e.g., hydroxyapatite, reinforced polyethylenecomposite, betatricalciumphosphate, substituted calcium phosphates,bioactive glass, resorbable calcium phosphate, alumina, zirconia, etc.that may be manufactured in a solid or mesh-like (described below)structure. It should also be noted that a biodegradable polymer can beused in combination with the bioceramic material to form a compositematerial to use as material 102. In the preferred embodiment, ahydroxyapatite material is utilized as the material 102 to form thepellet 100. It should be appreciated that the material 102 formingpellet 100 can be any type of material known in the art havingcharacteristics that result in non-toxic byproducts.

For example, pellet 100 can be formed of synthetic polymers (alone or incombination) such as polyurethanes, polyorthoesters, polyvinyl alcohol,polyamides, polycarbonates, poly(ethylene) glycol, polylactic acid,polyglycolic acid, polycaprolactone, polyvinyl pyrrolidone, marineadhesive proteins, and cyanoacrylates, or analogs, mixtures,combinations, and derivatives of the above. Pellet 100 can also beformed of naturally occurring polymers or natively derived polymers(alone or in combination) such as agarose, alginate, fibrin, fibrinogen,fibronectin, collagen, gelatin, hyaluronic acid, and other suitablepolymers and biopolymers, or analogs, mixtures, combinations, andderivatives of the above. Also, pellet 100 can be formed from a mixtureof naturally occurring biopolymers and synthetic polymers.Alternatively, pellet 100 can be formed of a collagen gel, a polyvinylalcohol sponge, a poly(D,L-lactide-co-glycolide) fiber matrix, apolyglactin fiber, a calcium alginate gel, a polyglycolic acid mesh,polyester (e.g., poly-(L-lactic acid) or a polyanhydride), apolysaccharide (e.g., alginate), polyphosphazene, or polyacrylate, or apolyethylene oxide-polypropylene glycol block copolymer. Pellet 100 canbe produced from proteins (e.g. extracellular matrix proteins such asfibrin, collagen, and fibronectin), polymers (e.g.,polyvinylpyrrolidone), or hyaluronic acid. Synthetic polymers can alsobe used, including bioerodible polymers (e.g., poly(lactide),poly(glycolic acid), poly(lactide-co-glycolide), poly(caprolactone),polycarbonates, polyamides, polyanhydrides, polyamino acids, polyorthoesters, polyacetals, polycyanoacrylates), degradable polyurethanes,non-erodible polymers (e.g., polyacrylates, ethylene-vinyl acetatepolymers and other acyl substituted cellulose acetates and derivativesthereof), non-erodible polyurethanes, polystyrenes, polyvinyl chloride,polyvinyl fluoride, poly(vinylimidazole), chlorosulphonated polyolifins,polyethylene oxide, polyvinyl alcohol, Teflon®, and nylon.

Bioceramics employed as material 102 within the pellet 100 can fall intoall three biomaterial classifications, i.e., inert, resorbable andactive, meaning they can either remain unchanged, dissolve or activelytake part in physiological processes. There are several calciumphosphate ceramics that are considered biocompatible and possiblematerials for the pellet 100. Of these, most are resorbable and willdissolve when exposed to physiological environments, e.g., theextracellular matrix. Some of these materials include, in order ofsolubility: Tetracalcium Phosphate (Ca₄P₂O₉)>Amorphous calciumPhosphate>alpha-Tricalcium Phosphate (Ca₃(PO₄)₂)>beta-TricalciumPhosphate (Ca₃(PO₄)₂)>>Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂). Unlike theother certain calcium phosphates listed above, hydroxyapatite does notbreak down under physiological conditions. In fact, it isthermodynamically stable at physiological pH and actively takes part inbone bonding, forming strong chemical bonds with surrounding bone. Thisproperty is advantageous for rapid bone repair after surgery. Otherbioceramic materials such as Alumina and Zirconia are known for theirgeneral chemical inertness and hardness. These properties can beexploited for implant device support purposes, where it is used as anarticulating surface for implant devices. Porous alumina can also beused as a bone spacer, where sections of bone have had to be removed dueto various conditions or diseases. The material acts as a scaffold ormatrix for bone growth.

FIG. 1B illustrates a cross-sectional portion of the pellet 100 having areinforced polymer and/or composite coating 110 that covers material 102of the pellet 100. For example, when pellet 100 comprises a bioceramicmaterial, polymer coating 110 comprises a polyactic acid or otherhydrogel, which may be formed according to ordinary methods. It shouldbe appreciated that polymer coating 110 does not have to be a completepolymer material, e.g., 100% polymer, but can be a composite materialcomprising a combination of any known bioceramic materials, compositehydrogels, and polymers. Moreover, the polymer coating can be made froma membrane such as collagen felt, or a similarly semi-rigid material,such as polylatic acid, polyether, etc. In the preferred embodiment,polymer coating 110 is a bio-resorbable polymer. The preferredbio-resorbable polymer exhibits characteristics such as favorablehandling properties that make the polymer easy to use (i.e., requires noadditional training for the operator to learn how to use, long-term,indefinite shelf life, economical, does not add considerable cost topatients, conforms to the receptor site, highly biocompatible andpartially biodegradable, low cost to manufacturer, biomimetic afterplacement, easy to distribute, space maintenance (maintains shape ofbone), supports cell growth and differentiation, chemotaxic properties(recruits wound healing host cells from surrounding tissue), andosteoconductive and osteoinductive). In addition, the polymer coatingserves the purpose of preventing contamination of material 102 whilesafe guarding, and not altering, the environment of an individual'smouth. The polymer coating 110 may be infused onto material 102 as aliquid or viscous gel substance.

Pellet 100 can also comprise an additional bone morphogenic protein(BMP) material by incorporating the BMP into material 102. Theadditional protein serves as a stimulus for bone growth, in other words,an additional mechanism by which the present invention promotesaccelerated bone growth within the pellet 100. The BMPs induce new bonegrowth within the pellet through a process resembling endochondral boneformation. In one embodiment, the BMP material comprises a proteinsubstance and is mixed into material 102 forming a composite pelletmaterial. The material 102 also can be infused with a collagen bonemorphogenic protein base. It should be appreciated that the proteinmaterial may also comprise other growth proteins. Fibrinogen,a-thrombin, as well as other various antibiotics, growth hormones, genetherapies, or combinations of these factors may also be utilized in thematerial 102 to promote healthy bone growth. The BMP material may beinfused within material 102 as a liquid or viscous gel substance.

It should be noted that pellet 100′ may comprise a material 102, asshown in FIG. 2 , having a mesh-like structure 230. The material 102 canbe constructed in a woven, mesh-like manner that allows the new bonegrowth to grow throughout the structure to form pellet 100′. Themesh-like structure 230, in comparison to a solid structure, provides agreater amount of exposed surface area for bone growth to occur. Themesh-like structure 230 has a porous nature; and its pores can besubstantially uniform or non-uniform. The mesh-like structure 230 ofpellet 100′ serves as a scaffold for the new bone growth. The pores canbe vertically arranged or horizontally arranged; the pores can bearranged in an organized fashion or randomly sized and arrangedaccording to the desires of the user.

At times, biodegradable polymers suffer from warping, hollowing orsubstantial erosion inherent with the process, of degradation. In orderto manage such a problem, polymers with high crystallinity are utilized.Self-reinforced and ultrahigh strength bioabsorbable composites arereadily assembled from partially crystalline bioabsorbable polymers,like polyglycolides, polylactides and glycolide/lactide copolymers.These materials have high initial strength, appropriate modulus andstrength retention time from 4 weeks up to 1 year in-vivo, depending onthe implant geometry. Reinforcing elements such as fibers of crystallinepolymers, fibers of carbon in polymeric resins, and particulate fillers,e.g., hydroxyapatite, may also be used to improve the dimensionalstability and mechanical properties of biodegradable devices. The use ofinterpenetrating networks (IPN) in biodegradable material constructionhas been demonstrated as a means to improve mechanical strength. Tofurther improve the mechanical properties of IPN-reinforcedbiodegradable materials, biodegradable plates may be prepared assemi-interpenetrating networks (SIPN) of crosslinked polypropylenefumarate within a host matrix of poly(lactide-co-glycolide) 85:15 (PLGA)or poly(l-lactide-co-d,l-lactide) 70:30 (PLA) using differentcrosslinking agents.

Resin composites with incorporated polytetrafluoroethylene (PTFE)particles improve the hydrophobicity and surface properties of deviceimplants, e.g., pellet 100. PTFE has high resistance to chemicalregents, low surface energy, tolerance to low and high temperatures,resistance to weathering, low friction wiring, electrical insulation,and slipperiness. However, because conventional PTFE has poor resistanceto abrasion, the inventor contemplates cross-linking PTFE withgamma-beam irradiation can be employed to drastically enhancesresistance to abrasion and deformation. Further, the composites made ofbraided carbon fibers and epoxy resins (so called biocompatiblecarbon-epoxy resin) have better mechanical properties than compositesmade of short or laminated unidirectional fibers.

FIGS. 3-5 show various stages of one particular application of thepellet according to the present invention. By way of example, thissequence of drawings shows the implantation of a pellet into a receptorsite, and the subsequent implantation of a dental implant into a newlygrown jaw bone. The exemplar implant device comprises a dental implantof a type that is commonly used today, e.g., a titanium implant or aceramic implant.

FIG. 3 shows a cross-section of bone 340 having an opening or cavity 360surrounded by an epithelial tissue layer 350. In the case of a dentalimplant, cavity 360 may represent the space created by avulsion of thenatural tooth previously occupying that space prior to extraction. Inother applications, the cavity 360 may be created by the removal ofeither damaged or healthy bone in order to provide an attachment sitefor the implant device. Cavity 360 can also be created by the removal ofcancerous tissue or tissue affected by any other type of disease capableof affecting the strength or shape of the tissue. Prior to inserting thepellet 100 into the cavity 360, the cavity 360 is cleaned and may beshaped utilizing conventional methods known in the art. As explainedabove, cavity 360 may be created by the removal of a natural tooth. Inother instances, cavity 360 may result from the defect of a long bonecreated, for example, by debritement of a dysplasila. Cavity 360 canalso result from any type of surgical procedure resulting in boneremoval or any type of procedure that creates any type cavity.

FIG. 4 shows the cross-section of FIG. 3 following insertion of thepellet 100 into cavity 360. Pellet 100 may be shaped to conform to thesize of the bone cavity 360. Once placed into cavity 360, the pelletremains secure within the cavity due to its polymer coating 110 (FIG.1B). Polymer coating 110 (FIG. 1B) interacts with the blood surroundingcavity 360 forming a securing mechanism, e.g., a blood clot, that allowspellet 100 to stay in place without the use of a barrier membrane (notshown). Barrier membranes have been conventionally used to seal dentalapplications into a cavity such as cavity 360. The barrier layer formedby the polymer coating 110 prevents mucosal attachment or soft tissuegrowth which would inhibit bone growth. Instead, osteointegration of newbone growth to and within the pellet 100 is permitted to occur. Itshould be noted that the use of pellet 100 is exemplary and any of theembodiments of the pellet can be used.

Once bone growth into the cavity 360 is complete, the region can be usedto support a prosthesis or may be cored or otherwise shaped to accept animplant device. FIG. 5 illustrates a bottom portion of an implant device680 fixably secured/attached to bone 340 using the newly grownosteointegration bone 690. The osteointegrated bone 690, consisting ofnew bone, provides improved fixation for implant 680 over the previouslyexisting deteriorated bone. Over time, it is expected that the bone 690will further integrate onto the outer, submerged surface layer ofimplant 680.

It should be appreciated that additional applications of the embodimentsof the invention exist for use in long bone or exo-augmentation. Forexample, this may involve the augmentation of bone onto the surface ofexisting skeletal bone. It is appreciated that the embodiments of theinvention are also useful in the treatment of a fractured or shatteredbone. The pellet material allows for bone integration at the damagedsite as well as soft-tissue attachment to the surrounding soft tissue.It is appreciated that the pellet may be shaped in a variety of sizes.That is, due to its semi-rigid nature, it may be molted or adapted tofit a particular application or circumstance.

The elastic bending moment capacity of un-fractured bone up to the onsetof plastic deformation (i.e., when stress in outer layer reaches yieldvalue) is about 320 Nm. Bending moment of 320 Nm induce about 0.5%strains in callus and 0.9% in composite plate. For comparison, themodulus of elasticity of typical metals used in osteosynthetic devicesis about 5 to 10 times that of bone which is 17-24 GPa. Callusformation, ossification and bone union are hampered by the lack ofstrain in bone. Braided composites deployed in this art should thereforebe just strong enough (up to 24 GPa with high stiffness to weight ratio)to promote the healing, but not so stiff as to hinder bone architecture.

As referenced above, three-dimensional printing, described in U.S. Pat.No. 5,204,055, is one method of creating complex geometries in medicaldevices. Three-dimensional printing is also described in U.S. Pat. No.5,370,692. Three-dimensional printing has been proposed for creating avariety of three dimensional medical devices, pharmaceuticals andimplants, however, the prior methods of creating a device did not relateto engineered microstructures. The biostructure of the embodiments ofthe invention may be manufactured by three-dimensional printingfollowed, in certain embodiments, by appropriate post-processing steps.Three-dimensional printing allows the manufacture of biostructures ofgreat geometric internal and external complexity including recesses,undercuts, internal voids and other geometric features, which aredifficult or impossible to create with conventional manufacturingprocesses. Three-dimensional printing also allows the creation ofcompositional variation within the biostructure that may not be achievedby conventional manufacturing processes.

In three-dimensional printing, a layer of powder is deposited such as byroller spreading. After the powder layer has been deposited, a binderliquid is deposited onto the powder layer in selected places so as tobind powder particles to each other and to already-solidified regions.The binder liquid may be dispensed in the form of successive discretedrops, a continuous jet, or other form.

Binding may occur either due to deposition of an additional solidsubstance by the binder liquid, or due to dissolution of the powderparticles or of a substance mixed in with the powder particles by thebinder liquid, followed by resolidification. Following the printing ofthe binder liquid onto a particular layer, another layer of powder isdeposited and the process is repeated for successive layers until thedesired three-dimensional pellet is created. Unbound powder supportsbound regions until the biostructure is sufficiently dry, and then theunbound powder is removed. Another suitable method that could be used todeposit layers of powder is slurry deposition.

The liquid thus deposited in a given pass binds powder particlestogether so as to form in the powder bed a line of bound material thathas dimensions of bound material in a cross-section perpendicular to thedispenser's direction of motion. This structure of bound powderparticles may be referred to as a primitive. The cross-sectionaldimension or line width of the primitive is related in part to thediameter of the drops if the liquid is dispensed by the dispenser in theform of discrete drops, or to the diameter of the jet if the liquid isdeposited as a jet, and also is related to other variables such as thespeed of motion of the printhead. The cross-sectional dimension of theprimitive is useful in setting other parameters for printing.

For printing of multiple adjacent lines, the line-to-line spacing may beselected in relation to the width of the primitive printed line. Alsotypically the thickness of the deposited powder layer may be selected inrelation to the dimension of the primitive printed line. Typical dropdiameters may be in the tens of microns, or, for less-demandingapplications, hundreds of microns. Typical primitive dimensions may besomewhat larger than the drop diameter.

Printing is also described by a quantity called the saturationparameter. Parameters which influence printing may include flow rate ofbinder liquid, drop size, drop-to-drop spacing, line-to-line spacing,layer thickness, powder packing fraction, etc., and may be summarized asa quantity called the saturation parameter. If printing is performedwith discrete drops, each drop is associated with a unit volume ofpowder that may be considered to have the shape of a rectangular prism.

In printing the described pellet, the at least one direction in whichthe unbound powder is not surrounded by bound powder provides access bywhich unbound powder can be removed after completion ofthree-dimensional printing. After drying of the three-dimensionalprinting biostructure, removal of unbound particles may first be done bysimple methods such as gentle shaking or brushing, and further removalof powder from the interior of macrostructures may be aided by the useof sonication in liquid or other convention techniques known in the art.Structures made by three-dimensional printing may include changes ofdirection, changes of cross-section, branchings, and the like.

There are also other possible ways of making the pellet. One such methodinvolves double-printing, i.e., printing on a layer of powder, allowingthe volatile part of the binder liquid to evaporate essentiallycompletely, and printing more binder liquid onto the same place suchthat the binder substance which remains after the last printing is builtup above the actual powder particles in the bed. The next layer ofpowder which is spread or deposited cannot occupy the region which isoccupied by the built-up binder substance from the “puddle” formed bythe repeat printing(s) at the same location. Eventually, when the bindermaterial in the puddle decomposes and exits as gaseous decompositionproducts, the absence of particles in the region formerly occupied bythe puddle yields a macrostructure of empty space. Yet another possiblemethod of making the pellet involves the chemical change of thecomposition of the powder particles. A second binder fluid that ischemically reactive may be printed in the region of the macrochannelsuch that the pellet is formed after burnout of the binder substance andchemical reaction of the particles with the chemically reactive bindersuch that the reaction product is soluble such as in water. Then,material in the macrochannel region may be dissolved or leached out toleave an open macrochannel.

What is claimed is:
 1. A pellet configured to preserve and augment bone,the pellet comprising: an inner material adapted to cause bone growth ina desired area, the inner material having a mesh-like structure andcomprising a bioceramic material and a biodegradable polymer, whereinthe biodegradable polymer comprises a partially crystallinebioabsorbable polymer comprising a polyglycolide, a polylactide, or aglycolide/lactide copolymer; and a polymer coating completelysurrounding and covering the inner material, wherein the pellet is sizedto fill a bone extraction site as one piece, and the polymer coatingcomprises a polymer and a bioceramic material.
 2. The pellet of claim 1,wherein the bioceramic material of the inner material comprises calciumphosphate.
 3. The pellet of claim 1, wherein the bioceramic material ofthe inner material comprises hydroxyapatite.
 4. The pellet of claim 1,wherein the bioceramic material of the inner material comprisestricalcium phosphate.
 5. The pellet of claim 1, wherein thebiodegradable polymer further comprises a reinforcing material or aninterpenetrating network (IPN), or both, to improve dimensionalstability.
 6. The pellet of claim 5, wherein the reinforcing material ispresent in the biodegradable polymer and comprises a plurality ofcrystalline polymer fibers, a plurality of carbon fibers, or both, toincrease dimensional stability of the pellet.
 7. The pellet of claim 1,wherein the bioceramic material of the inner material compriseshydroxyapatite and the inner material further comprisespolycaprolactone.
 8. The pellet of claim 1, wherein the polymer coatingfurther comprises a hydrogel.
 9. The pellet of claim 1, wherein thepellet comprises a cylindrical, elliptical, or rectilinear lateralcross-sectional shape.
 10. A pellet configured to preserve and augmentbone, the pellet comprising: an inner material adapted to cause bonegrowth in a desired area, the inner material having a mesh-likestructure and comprising a bioceramic material and a biodegradablepolymer, wherein the biodegradable polymer comprises a partiallycrystalline bioabsorbable polymer comprising a polyglycolide, apolylactide, or a glycolide/lactide copolymer; and a polymer coatingcompletely surrounding and covering the inner material, wherein thepolymer coating comprises a polymer and a bioceramic material.
 11. Thepellet of claim 10, wherein the bioceramic material of the innermaterial comprises calcium phosphate, hydroxyapatite, or tricalciumphosphate.
 12. A pellet adapted to preserve and augment bone, the pelletcomprising: an inner material adapted to cause bone growth in a desiredarea, the inner material having a mesh-like structure and comprising abioceramic material and a biodegradable polymer, wherein thebiodegradable polymer comprises a partially crystalline bioabsorbablepolymer comprising a polyglycolide, a polylactide, or aglycolide/lactide copolymer; and a polymer coating completelysurrounding and covering the inner material, wherein the polymer coatingcomprises a bioceramic material, a hydrogel, and a polymer.
 13. Thepellet of claim 12, wherein the bioceramic material of the innermaterial comprises calcium phosphate, hydroxyapatite, or tricalciumphosphate.
 14. The pellet of claim 12, wherein the biodegradable polymerfurther comprises a reinforcing material to improve dimensionalstability of the pellet.
 15. The pellet of claim 12, wherein the pelletcomprises a cylindrical, elliptical, or rectilinear lateralcross-sectional shape.